Field of the Invention
The invention relates to a circuit configuration for detecting undervoltage of a voltage source, including a reference voltage source being fed by the voltage source and having an output being supplied to a first input of a comparator, a voltage divider for dividing a voltage furnished by the voltage source having an output being supplied to a second input of the comparator, and the comparator having an output at which a detection signal can be tapped.
Especially in battery-powered devices, a circuit configuration for detecting undervoltage performs an important function. In order to detect undervoltage, a comparator and a reference voltage source are used in most cases. However, the reference voltage source is usually supplied from the same voltage source, namely the source that is to be monitored. Such a configuration is shown in FIG. 3 and described in greater detail below. In practice that configuration presents problems if a reference voltage source is supplied from the same voltage.
Another such monitoring circuit is shown in German Published, Non-Prosecuted Application DE 34 03 798 A1, corresponding to U.S. Pat. No. 4,618,780, in which a proportional voltage being referred to the supply voltage and generated through the use of a voltage divider is compared in a comparator with a reference voltage.
In German Published, Non-Prosecuted Application DE 32 38 544 A1, corresponding to U.K. Application GB 2 108 342 and in European Application 0 207 159 A1, comparator circuits are described that contain a switching device through the use of which the output of the comparator can be enabled for voltage monitoring. U.S. Pat. No. 3,670,246 describes a circuit for voltage monitoring, in which undesired emission of a signal when the voltage source is turned on is prevented by using a capacitor that delays the switching of the comparator stage in a defined manner.